Giant Lattices (Edexcel AS Chemistry): Revision Note

Giant Lattices

Types of Giant Lattice

• Most ionic, metallic and covalent solids exist as giant lattice structures

  • A lattice is regular, repeating three-dimensional arrangement of ions or atoms extending throughout the solid

• There are three main types:

  1. Giant ionic lattices

  2. Giant metallic lattices

  3. Giant covalent lattices

Ionic Lattices

• The ions form a lattice structure which is an evenly distributed crystalline structure

• Ions in a lattice are arranged in a regular repeating pattern so that positive charges cancel out negative charges

• The attraction between the cations and anions is occurring in all directions

  • Each ion is attracted to all of the oppositely charged ions around it

• Cations and anions are arranged in a regular repeating three-dimensional structure

  • This means that the positive and negative charges cancel each other out

  • Therefore the final lattice is overall electrically neutral

• The arrangement depends on the relative sizes of the ions and the ratio of cations to anions

• In sodium chloride (NaCl):

  • Each Na⁺ ion is surrounded by 6 Cl^- ions

  • Each Cl^- ion is surrounded by 6 Na⁺ ions

  • This is 6 : 6 coordination

    • This simplifies to 1 : 1, which is why the formula of sodium chloride is NaCl

• The NaCl lattice is cubic; magnesium oxide (MgO) adopts the same arrangement

• Electrostatic attraction between oppositely charged ions acts in all directions

Ionic solids are arranged in lattice structures

Metallic Lattices 

• Positive metal ions (cations) are arranged in a regular pattern, surrounded by a sea of delocalised electrons

• Metallic bonding is the strong electrostatic attraction between the cations and the delocalised electrons

• The cations are arranged in close-packed layers

  • Either hexagonal or cubic close-packed

• The strength of metallic bonding increases with:

  • Greater charge on the metal cation

  • Smaller ionic radius

  • Greater number of delocalised electrons per atom

• The layered structure with the delocalised electrons gives a metal its key properties

Layers of copper ions (the delocalised electrons are not shown in the diagram)

Covalent lattices

• Covalent bonds are bonds between nonmetals in which electrons are shared between the atoms

• Covalent compounds can be arranged in simple molecular or giant molecular lattices

  • Simple molecular lattices:

    • Iodine

    • Buckminsterfullerene (C₆₀)

    • Ice

  • Giant molecular:

    • Silicon(IV) oxide

    • Graphite
      Diamond

Simple molecular lattices

Giant molecular lattices

Comparing Giant Lattices